a. Field of the Invention
This invention relates to portable cards for systems for processing signals, and to a method of manufacturing such cards.
b. Description of the Prior Art
In most applications where an article is used to give a person private access to a system, this article more and more frequently takes the form of a portable card such is the case with credit cards, for example, which have been in use for some twenty years and are not widespread.
Recently, the International Standards Organisation laid down rules for the dimensional characteristics of credit cards (ISO/DIS standard 2894). Standard cards are to be in the shape of a rectangle 85.72 mm by 55.98 mm and 0.762 mm thick. The alpha-numeric characters which are intended for example to indicate the name and address of the person to whom the card belongs, expiry information, etc. may be embossed formations whose height relative to one of the faces of the card should not exceed approximately 0.5 mm.
In the usual present-day cards, information other than these alpha-numeric characters which is intended to give the card-holder access to a system for processing electrical signals is contained solely on prerecorded magnetic strips or bands which are attached to the card. Although what is contained on the bands may be adequate in certain applications, it is inadequate for other applications. For example, in credit card applications, it would be of great advantage to expand the information and to incorporate in the card processing circuits which are capable of dialog with the signal processing system and which may possibly include a memory. With such circuits credit cards could, in particular, perform required debit and/or credit operations in conjunction with the processing system and could record the results of these operations.
A number of trials have been carried out along these lines in which attempts have been made to incorporate an integrated circuit device in the card and have brought to light problems in such applications for credit cards. For example, small thickness (0.762 mm) called for by the international standard still has to be sufficient to accommodate an integrated circuit device capable of performing the aforementioned operations, while at the same time the card has to retain a certain amount of flexibility without jeopardizing the operation of the device.
A number of embodiments of credit card incorporating integrated circuits are known. In one such embodiment, the capsule containing the integrated circuit is connected to an array of conductors formed on a rectangular sheet of given length, the conductors terminating in contact areas which extend across part of the width of the sheet. A second sheet, of the same thickness as the capsule, contains an opening of the same length and breadth as the capsule but is not so long as the first sheet so as to leave the aforesaid contact areas exposed. This second sheet is applied to the first sheet so as to enclose the capsule. Finally a third sheet, of the same length and breadth as the second sheet, covers the second sheet and the capsule.
A drawback of this type of credit card and the method of producing the credit card is that it involves three sheets of different configurations which have to be correctly superimposed and then bonded or welded. Also, because the card must meet the standard mentioned above, the total thickness of the three sheets must not exceed 0.762 mm and the sheets thus have to be exceedingly thin, making them difficult to handle. Further the capsule necessarily also has to be very thin and special techniques have to be used for the bonding or welding.
In another known embodiment of credit cards incorporating integrated circuits, the card is produced from only two sheets. One of the faces of the first sheet is provided with an array of conductors which terminate in an equal number of external contact areas and the integrated circuit device is applied to this first sheet. The second sheet is arranged on top of it, but in order that the card will encapsulate the said device, the two sheets are made of a material which softens at high temperature. Thus, by heating the sheets to this temperature, the two sheets may be welded together with the device contained within them. This type of assembly thus calls for the use of two sheets made of a material having closely defined characteristics and then for controlled welding to take place at a high temperature. Subjecting the integrated circuit to high temperatures is undesirable in that it might affect the condition of the device.
The present invention substantially reduces or overcomes all of these drawbacks and disadvantages.